Iron rivals platinum as fuel-cell catalyst

A limiting factor in hydrogen fuel-cell performance is the slowness of the oxygen-reduction reaction that occurs at the cathode. Platinum is an effective catalyst for promoting that reaction, but it is both expensive and scarce. The performance of alternatives based on transition metals such as iron or cobalt has been disappointing to date. Now experimenters led by Jean-Pol Dodelet at Canada’s Institut National de la Recherche Scientifique have found a way to make an Fe-based catalyst that rivals Pt. The current density of a fuel cell made from the new catalyst can equal that of a Pt-based fuel cell at cell voltages ≥ 0.9 V. The method used by Dodelet and coworkers is the culmination of systematic research that delineated the key steps to making the catalyst. One step was to use a ball-milling technique to force iron acetate and another ingredient (PTDA or phenanthroline) into the micropores of carbon-black particles (see the figure). Challenges still lie ahead. Below 0.9 V, the voltage of fuel cells made from the new Fe-based catalyst falls off too rapidly with increasing current density, largely because the diffusion of oxygen into the catalytic sites is not optimized. And the lifetime of the catalysts is limited by the instability of its materials. Still, those working on such alternative catalysts are greatly energized by the new results. (M. Lefèvre et al., Science 324, 71, 2009.) — Barbara Goss Levi